The field of the invention pertains to mechanical power transmission through electromagnetic clutches and couplings, and, in particular, to clutches and couplings that utilize a large plurality of steel balls contained within one or more chambers.
An example of a clutch or coupling utilizing balls is U.S. Pat. No. 5,163,873 to the applicant wherein coaxial shafts are coupled and uncoupled by a large plurality of balls in a pair of annular chambers that surround one of the shafts. A first wall of each chamber is formed by a hollow concentric shell affixed to rotate with the other shaft, and a second concentric wall of each chamber is movable in response to the squeezing of a magnetically actuated spiral coil. Magnetic actuation of the spiral coil causes the movement of the second concentric walls to squeeze the balls tightly against the first shaft and the first concentric wall of the shell thereby providing a driving engagement between the first and second shafts.
Although a workable coupling or clutch for many applications, the above device employs a relatively large external electromagnet to actuate the spiral coil. The electromagnet comprises an appendage located outside of the concentric shell, thus greatly increasing the overall diameter of the device and effectively preventing its use inside an electric motor, for example. To provide an electromagnetically operable coupling or clutch of compact size, applicant has developed the device disclosed below.
Most of the present power transmission clutches, in particular for vehicles, are based on principles of friction. Friction disc packs, bands, hydraulic pistons and cylinders and splined disc drive members are employed under the control of computer generated commands to operate various valves or ports. When a vehicle accelerates or decelerates through shift points, the disc packs or bands slip generating considerable heat which must be dissipated and limiting the life of the friction parts.
The new ball coupling or clutch comprises a plurality of magnetizable balls located between inner and outer concentric caged needle rollers without raceways. The caged needle rollers are concentric with the axis of a hollow non-magnetic rotatable shaft which carries therewithin an actuateable electromagnet. Substantially surrounding the caged needle rollers and balls to form chambers therefor is a rotatable concentric shell of a non-magnetic material. Upon actuation of the electromagnet, the balls and needle rollers magnetically nest together to form a torque transmitting condition between the hollow shaft and the shell. A third set of needle rollers mounted in the wall of the hollow shaft allows the electromagnet to float in a non-rotating condition within the rotating hollow shaft. The configuration of the new coupling or clutch is ideally suited for incorporation within an electric motor without external appendages or significant increase in overall diameter of the motor.
Since the new coupling or clutch does not rely upon friction to transmit torque, heat generation is limited and heat more easily removed by air or other fluid convection among the balls and rollers in addition to heat conduction through contact among the balls and rollers. Whether free-running or locked up, there are open spaces for fluid flow throughout the ball and roller clusters thereby providing every contact point within the clusters with fluid cooling. Choice of air, oil or water does not significantly change the torque rating of the coupling or clutch because the oil or water film cannot withstand the very high pressures on the very small contact points among the curved surfaces of the balls and rollers. Wear is minimized and spalling prevented by the very large number of balls and rollers which create a very large number of contact points.
Experimental testing has revealed that the electrical control of the electromagnet is linear between the extremes of free running and fully locked-up torque transmission. With sufficient magnetism applied, rated torque xe2x80x9clock-upxe2x80x9d is maintained. When the magnetic field is turned off, the ball and roller cluster rapidly returns to the free-running state. The coupling or clutch can tolerate high magnetic coil current xe2x80x9cimpulse torquesxe2x80x9d of short duration several times greater than normal rated torque. Cyclic testing has also shown that wear of the working parts of the coupling or clutch is minimal largely due to the rolling contact among the balls and rollers, the hardened steel surfaces of the contacting balls and rollers and low heat retention of the configuration.
The new coupling is ideally suited for electric vehicle drives; specifically, for xe2x80x9cin the wheelxe2x80x9d induction motor planetary drives. A pure electric vehicle with a D.C. powered, solid state, adjustable frequency alternating current source eliminates the need for a main engine, drive train, differentials or universal joints. Where a hybrid vehicle is required, the gasoline or diesel engine need only drive a D.C. or A.C. generator of sufficient capacity. The new coupling or clutch is ideally suited to straightforward solid state control with the coupling or clutch and the electric motor operated for maximum torque or maximum efficiency as desired.